I do happen to think the JLPT has some big flaws, but nonetheless - it’s surely better if someone like you who knows Japanese but hasn’t prepared specifically for the test can pass it. It would be more troubling if it weren’t potentially feasible for anyone to pass, because that would be a very badly-designed exam.
To your earlier point, I don’t understand why you say you lost respect for it because “anyone could pass it”… anyone can pass just about any exam with enough time and/or motivation. I’m not sure if I’m ready for N1 in July (plus it clashes with a conference I’m supposed to go to…). Unfortunately the JLPT is the only test it’s practical for me to take in Europe. (By the way, it's scaled so the percentage score is next to meaningless.) And I was so worried I’d failed… I'm especially surprised that my highest score was in listening and lowest in grammar/vocab, I would have predicted the opposite. If I had to take the test based on what I have sat down and formally studied I very seriously doubt I could pass N3. I passed the test strictly on the strength of massive amounts of exposure. What is wanted in most cases, I think, is simply greater exposure to the language and more active interaction using the language. Get your listening practice in situations that require you to be an active participant instead of just a passive listener. Read lots of stuff without looking things up. Try to work in as much real-life practical application as you can. I did alright on the listening because I'm surrounded by people who speak nothing but Japanese and I'm expected to at least kinda-sorta keep up with what's going on and function in that environment. I did well on the reading because I have read stacks of Japanese books and read lots of various stuff just in the course of work and daily life. I got better scores on the sections where studying really can't help all that much. I think that got reflected in my lower score on the part of the test that would benefit the most from studying.
I can't speak as to the value of study, since I really have done very little studying of Japanese.